A disk-like recording medium used for recording and reproducing information signal by using a light beam (hereinafter simply referred to as an optical disk) includes a read-only optical disk such as a so-called compact disc, a write-once optical disk on which data can be recorded only once, and a recordable type optical disk from which data can be not only reproduced and but also which data can be recorded and erased.
The read-only optical disk has, on one surface, a track where concave and convex patterns, i.e., phase pits are centrically or spirally formed in response to recorded information signal. Specifically, Such optical disk is formed of a disk substrate made of synthetic resin material such as poly carbonate, PMMA or the like having light transmittance, a reflective film made of Al, Au or the like and formed so as to cover the phase pits formed on one surface of the disk substrate, and a protective layer formed so as to cover the reflective film in order to protect the reflective film.
When an information signal is reproduced from the read-only optical disk, a light beam from a laser light source is irradiated from the disk substrate side with being converged by an objective lens. A luminous flux of reflected light modulated depending upon the phase pit of this optical disk is detected by a photodetctor, for example, and converted into a detection signal having a signal level in response to a light amount of the luminous flux of the reflected light. Thus, a reproduced signal of the information signal recorded on the read-only optical disk is obtained.
A magneto-optical disk employing a vertically magnetized recording material and so on is known as the recordable type optical disk. The magneto-optical disk is formed of a disk substrate made of synthetic resin material such as polycarbonate, PMMA or the like having light transmittance and having a guide groove for guiding the light beam formed on one surface thereof, a recording layer formed so as to cover the above guide groove and made of a vertically magnetized recording material such as Te, Fe, Co or the like, and a protective layer formed so as to cover the above recording layer in order to protect the recording layer.
When a desired information data is recorded on this magneto-optical disk, the desired information data is subjected to a predetermined modulation to thereby generate a recording signal. This generated recording signal is supplied to a magnetic-field generating device, for example. Then, the magnetic-field generating device applies an external magnetic field corresponding to a recording signal to the magneto-optical disk, thereby a portion irradiated with the laser light from an optical head a portion that is heated to a temperature higher than a Curie temperature) of a vertical magnetized film (recording layer) of the magneto-optical disk being magnetized in response to the recording signal. Thus, the information data is recorded.
When the information data is reproduced from the magneto-optical disk, similar to the reproduction of the above read-only optical disk, a light beam from a laser light source is irradiated thereon from the side of the disk substrate with its being converged by an objective lens. A recording signal recorded on the magneto-optical signal is reproduced by detecting a Kerr rotation angle in the luminous flux of the reflected light modulated by a recording layer of the optical disk, and the reproduced signal is subjected to a predetermined demodulation. Thus, the information data is reproduced.
The write-once optical disk includes one of a recording system utilizing physical and chemical change of a pigment, one of a recording system in which an aperture is formed through a single-layer film, one of a recording system in which an aperture is formed through a multilayer film, one of a phase change recording system, one of a bubble forming recording system and so on. When the write-once optical disk is reproduced, similar to reproduction of the above read-only optical disk, a light beam (having a weak optical output for reproduction) from a laser light source is irradiated from the disk substrate side with it being converged by an objective lens. A luminous flux of reflected light modulated depending upon the previously recorded phase pit is detected by a photodetctor, for example, and converted into a detection signal having a signal level in response to a light amount of the luminous flux of the reflected light. Thus, a reproduced signal of the information signal recorded on the read-only optical disk is obtained.
When the information data is recorded on and reproduced from the magneto-optical disk, it is necessary to precisely set at least a phase of a channel clock (sampling clock) used for modulation and demodulation processing timings in order to precisely record the above recording signal on the magneto-optical disk and to obtain precise information data from the signal reproduced from the magneto-optical disk.
The assignee of the present invention has proposed a system of detecting a clock of an optical disk which enables precise detection of the channel clock (see Japanese laid-open patent publication No. H3-156774, the disclosure of which is incorporated herein by reference).
FIG. 6 shows an arrangement employed when the system for detecting the clock of the optical disk is applied to a magneto-optical disk recording and reproducing apparatus. Specifically, as shown in FIG. 7, the magneto-optical disk used in the magneto-optical disk recording and reproducing apparatus has servo areas in each of which a servo pattern having a pair of wobble pits WP1, WP2 displaced respectively toward inner and outer periphery sides from a center of a track TR centrically formed and a clock pit CP positioned at the head of a pair of wobble pits WP1, WP2 are disposed at a predetermined interval.
There are one thousand and four hundred servo areas in one round of the magneto-optical disk. Data area is provided between a servo area and the next servo area. In this data area, a sub code such as a synchronization data, an address data or the like and the recording signal subjected to a predetermined modulation are magneto-optically recorded.
The magneto-optical recording and reproducing apparatus shown in FIG. 6 has a spindle motor for rotating a magneto-optical disk 101 having the above format at a CAV (constant angular velocity) similar to that employed when the recording signal is recorded, an optical system 102 for irradiating laser light on the magneto-optical disk 101 rotated by the above spindle motor 100 and for detecting return light therefrom to output it as a reproduced signal, an RF amplifier 105 for amplifying the reproduced signal from the optical system 102 with a predetermined gain, an A/D converter 106 for converting the amplified reproduced signal from the RF amplifier 105 into a digital reproduced signal, a latch circuit 107 for holding the reproduced data from the above A/D converter 106 at a predetermined latch timing, a phase error detector 108 for detecting a phase error of the channel clock relative to the reproduced data based on respective values of the reproduced data held by the latch circuit 107 to output it as a phase error detection data, a D/A converter 109 for converting the phase error data from the above phase error detector 108 into an analog phase error detection from the above phase error detection signal, a phase compensator circuit 110 for removing a high-band noise component of the phase error detection signal from the D/A converter 109 to thereby keep stability of a PLL, a voltage-controlled oscillator (VCO) 111 for changing an oscillation frequency in response to a voltage level of the phase error detection signal supplied from the above D/A converter 109 through the phase compensator circuit 110, and a feed-back loop for feeding the channel clock output from the VCO 111 back to the A/D converter 106 at a first stage.
In the conventional recording and reproducing apparatus, before the recording signal recorded on the magneto-optical disk 101 is reproduced or before the recording signal is recorded on the magneto-optical disk 101, a phase based on detection of the servo pattern and the phase of the channel clock are previously set so as to be matched with each other (servo pattern detection mode). When the mode is brought into servo pattern detection mode, the optical system 102 irradiates the laser light on the magneto-optical disk 101 rotated by the spindle motor 100 and detects the returning light therefrom to subject it to photoelectric conversion, thereby the servo pattern and the recording signal recorded on the magneto-optical disk 101 are reproduced therefrom. The reproduced signal is amplified by the RF amplifier 105 at the succeeding stage and then supplied to the A/D converter 106, wherein the reproduced signal is converted into digital reproduced data. The A/D converter 106 samples the above amplified reproduced signal with the channel clock supplied from the VCO 111 through the feed-back loop to thereby convert the reproduced data into the digital reproduced data.
Since, as shown in FIG. 7, the above servo pattern formed in the servo area is formed of a pair of wobble pits WP1 and WP2 and one clock pit CP, as shown in FIG. 8A, a waveform of the reproduced data of the above servo pattern is a waveform continuously having a signal waveform SW1 of the clock pit CP having a very high level at the head thereof and signal waveforms SW2 and SW3 of the two wobble pits WP1, WP2 each having a level lower than that of the signal waveform SW1 of the clock pit CP.
If the channel clock output from the VCO 111 has a precise phase and an operation of counting the above channel clock is started after the detection of the above servo pattern, then it is possible to precisely latch the servo pattern by latching the reproduced data from the A/D converter 106 when the count value becomes one value within the range from n to n+2 and n+5 to n+7.
Therefore, the conventional recording and reproducing apparatus is designed to incorporate a servo pattern detecting circuit, a counter and a latch pulse outputting circuit which are not shown. The servo pattern detecting circuit is a circuit for comparing data with respect to the servo pattern previously stored with the reproduced data from the A/D converter to thereby detect the servo pattern. The servo pattern detecting circuit detects the servo pattern to thereby output a detection pulse to the counter.
The counter is a circuit for resetting, based on an input of the detection pulse from the servo pattern detecting circuit, a count value thereof and for starting an operation of counting the above channel clock from this point.
The latch pulse outputting circuit is a circuit which incorporates a count value comparing circuit and which outputs to the latch circuit 107 a latch pulse at every time when the count value successively supplied thereto from the counter becomes a value within the range of from n to n+2 and the range of from n+5 to n+7.
The latch circuit 107 latches the reproduced data from the A/D converter 106 at a timing based on the input of the latch pulse successively supplied from the latch pulse outputting circuit, thereby data values at points indicated by points a1, a0, a2, c1, c0 c2 in FIG. 8A are held. These data values are supplied to the phase error detector 108 at the succeeding stage.
When supplied with the data value from the latch circuit 107, the phase error detector 108, by utilizing symmetry of each of the waveforms SW2 and SW3 at the two servo pits WP1 and WP2, detects a phase error of the channel clock relative to the reproduced data of the above servo pattern in accordance with the following equation (1) based on differences between levels at the points a1, a2 and the points c1, c2 which are respectively shoulder points located away from the points a0, c0 shown in FIG. 8 that are center points of the waveforms SW2 and Sw3 by one channel clock amount in both directions. Then, the phase error detector supplies the phase error as the phase error detection data to the D/A converter 109. EQU phase error data=[(a2-a1)+(c2-c1)]/2 (1)
The reproduced data of the servo pattern is also employed not only for generating the above phase error data but also for generating a tracking error signal, a detection signal of a mean level of wobble pits, a mirror-portion level detection signal and so on in accordance with the following equations (2) to (4). EQU tracking error signal=c0-a0 (2) EQU mean level detection signal=(a0+c0)/2 (3) EQU mirror-portion level detection signal=d0 (4)
The above D/A converter 109 converts the phase error detection data output from the phase error detector 108 into an analog signal to generate a phase error detection signal, and supplies it to the phase compensator circuit 110 at the succeeding stage. Te phase compensator circuit 110 is formed of an integrator, primary filter and so on, and removes the high-band noise component of the supplied phase error detection signal to thereby phase-compensate the phase error detection signal, and then supplies the phase-compensated phase error detection signal to the VCO 111 at the succeeding stage.
The VCO 111 can change its oscillation frequency based on the voltage level of the phase error detection signal, thereby feeding back to the A/D converter 106 through the feedback loop the channel clock having a frequency which permits the phase error of the channel clock relative to the reproduced data of the servo pattern to be set to zero.
Specifically, a block for generating the channel clock in the recording and reproducing apparatus for the magneto-optical disk 101 is arranged as a so-called PLL arrangement, and outputs the channel clock having a phase synchronized with the phase of the reproduced data of the above servo pattern.
The channel clock output from the above VCO 111 is also supplied to a demodulating circuit 103 of a data reproducing system in the recording and reproducing apparatus and to a modulating circuit (not shown) of the data recording system.
Thus, in the recording and reproducing apparatus, the VCO 111 outputs the channel clock having the phase synchronized with the phase of the reproduced data of the above servo pattern. Specifically, when an operation of locking the phase of the reproduced data of the servo pattern is finished, the servo pattern detection mode is finished, and then the processing proceeds to a reproduction mode for reproducing the recording signal recorded on the magneto-optical disk 101 or a recording mode for recording the recording signal on the magneto-optical disk 101.
When the processing of the recording and reproducing apparatus is brought into the reproduction mode, the recording signal recorded on the magneto-optical disk 101 is read out therefrom by the optical system 102. The reproduced signal from the optical system 102 is supplied through the RF amplifier 105 to the A/D converter 106 as described above and also to the demodulating circuit 103 in the data reproduction system.
The above A/D converter 106 samples the amplified reproduced signal from the RF amplifier 105 at a clock timing of the channel clock supplied thereto through the feed-back loop and converts it into the digital reproduced data to supply the latter to the latch circuit 107 at the succeeding stage. Thus, the latch circuit latches data with the respect to the servo pattern of the reproduced data. the phase error detector generates the phase error detection data based on the latch data. Based on the phase error detection data, the oscillation frequency of the VCO 111 is repeatedly and variably controlled.
The demodulating circuit 103 demodulates the amplified reproduced signal from the RF amplifier based on the channel clock from the VCO 111 to obtain information data, and outputs the information data through an output terminal 104 to an interface circuit connected to the host computer at the succeeding stage and to a D/A converter connected to a speaker apparatus at the succeeding stage.
When on the other hand the processing of the recording and reproducing apparatus is brought into the recording mode, the information data supplied from the host computer, for example, through the interface circuit is supplied to the modulating circuit. The modulating circuit modulates the information data from the interface circuit based on the channel clock from the VCO 111 to obtain the recording signal, and then supplies the recording signal to the external magnetic-field generating device. The external magnetic-field generating device changes a magnetization direction in response to the supplied recording signal, thereby the recording signal being recorded on the magneto-optical disk as the magnetization information.
At this time, the reproduced signal generated based on the returning light from the servo area detected by the optical system 102 is supplied through the RF amplifier 105 to the A/D converter 106. Similarly to the operation of the reproduction mode, the oscillation frequency of the VCO 111 is repeatedly and variably controlled based on the phase error detection data from the phase error detector 108.
As described above, since the phase of the channel clock output from the VCO 111 is synchronized with the phase of the above servo pattern, it is possible for the demodulating circuit 103 to precisely demodulate the reproduced signal , and also it is possible for the modulating circuit to precisely modulate the information data to obtain the recording signal.
However, it is sometimes observed that the magneto-optical disk has a defect produced on a servo pattern during its manufacturing process or under conditions of use thereof. If the servo pattern has any defect, it is difficult to precisely to detect the servo pattern.
If production of such defect disables the detection of the servo pattern or leads to imprecise detection thereof, then the phase of the channel clock is considerably mismatched with the phase of the reproduced data of the servo pattern, and hence the operation of latching the reproduced data by the latch circuit 107 is carried out at a position displaced from both of the shoulders of the data waveforms SW2, SW3 of the wobble pits WP1 and WP2 as shown in FIG. 8B.
In this state, it is not possible for the phase error detector 108 to generate the precise phase error detection data, and hence it becomes impossible for the VCO 111 to output the channel clock having the frequency precisely synchronized with the phase of the reproduced data of the servo pattern.
Since, as described above, the above channel clock is used when the information data is recorded on and reproduced from the magneto-optical disk 101, if the channel clock is not precise, then precise recording and reproduction may not be carried out.
In view of the above, it is an object of the present invention to provide a disk apparatus and recording and reproducing method therefor which, even if a disk-like recording medium has any defect and external disturbance of the defect disturbs a reference-clock generating loop (PLL) and increases the phase error, can detect a state in which the phase error is large and avoid an operation of recording data on the disk-like recording medium based on an abnormal reference clock.
It is another object of the present invention to provide a disk apparatus and recording and reproducing method therefor which, even if the external disturbance resulting from the defect on the disk-like recording medium leads to imprecise detection of the phase error, can prevent the above external disturbance from influencing generation of the reference clock and avoid generation of the reference clock having the imprecise phase.
It is further another object of the present invention to provide a disk apparatus and recording and reproducing method therefor which can take the difference between permissible phase errors at the inner and outer peripheries of the disk-like recording medium into account when the reference clock is generated and can carry out, in response to an access position to the disk-like recording medium, a most suitable interlocking processing (a processing for inhibiting an operation of recording data on the disk-like recording medium when the phase error exceeds the tolerance of the phase error).